The main cost is hard drive. We’re looking about 2.5
GiB + database size per build, as opposed to the relatively
small footprint of a standard Odoo deploy. While we could
theoretically strip the base system down to probably under 2
gigs, there will still always be the cost of having the system
included in the build.

That said, this hard drive penalty comes with a big
gain - builds are truly isolated in terms of OS and Python
dependencies, providing a more true to life picture of how
modules will operate in the wild using what we specify in the
readable source.